This might be too specific to work for everyone, but what worked to boost my self esteem and confidence was taking classes to build my voice. For me, those classes were singing lessons. I understand that many people are scared of taking them because they fear being bad, but usually that is not what it's about. Also, if I can embarrass myself by stuttering, I might aswell embarrass myself by singing lol. It helped me to get honest feedback on what I'm doing wrong and should practice. Realizing that I have a voice that can be loud and demand attention is awesome aswell. Should you consider this just be upfront with your teacher and tell them why you are there (building your voice in the first place), it can help them in their work with you.